CHAPTER IV. 



HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE 



TISSUES. 



i. EPITHELIAL TISSUE. 



The epithelial tissue consists of one or more layers of cells 

 resting on a homogeneous membrane, the other side of which is 

 abundantly supplied with blood-vessels and nerves. The form 

 of the epithelial cell varies in different situations, and may be 

 flattened, cuboid, spheroid, or columnar. (See Figs. 4, 5, and 6.) 

 The form of the cell in all instances is related to some specific 

 function. When arranged in layers or strata, the cells are cemented 

 together by an intercellular substance. 



FIG. 4. EPITHELIAL CELLS OF RABBIT, ISOLATED. X 560. i. Squamous cells 

 (mucous membrane of mouth). 2. Columnar cells (corneal epithelium). 3. 

 Columnar cells, with cuticular border, 5 (intestinal epithelium). 4. Ciliated cells; 

 h, cilia (bronchial epithelium). 



The epithelial tissue forms a continuous covering for the surfaces 

 of the body. The external investment (the skin) and the internal 

 investment (the mucous membrane, which lines the entire alimentary 

 canal and its associated body cavities) are both formed, in all situa- 

 tions, by the homogeneous basement membrane, covered with one 

 or more layers of cells./' Alljra^^ 



secretory, or excretory, must pass through epithelial cells before they 

 can enter into the formation of the tissues or be eliminated from them 

 The nutrition of the epithelial tissue is maintained by the nutritive 

 material derived from the blood diffusing itself into and through 

 the basement membrane. Chemically, the epithelial cells of the 

 epidermis hair, nails, etc. are composed of an albuminoid material 



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